Structural components in aerospace and underwater vehicle systems contain fluids or bear mechanical loads. They add mass to the vehicle, which reduces the amount of onboard propellant the vehicle is able to carry. This in turn limits the payload weight that the vehicle is able to carry as well as its endurance, range, and/or velocity.
In current aerospace and underwater vehicle systems, structural components are often sized to withstand the acceleration and vibration loads encountered during launch. After launch, the vehicle experiences relatively insignificant loads and much of the mass of the structural components is unnecessary, particularly for those vehicles which are expendable, non-serviceable, or non-reusable. In those cases, the momentum associated with the structural mass constrains maneuverability and can limit mission performance.
Past attempts at utilizing structural mass after launch include the use of thermoplastics (e.g., fluoropolymers such as polytetrafluoroethylene, which is currently used in pulsed plasma thrusters). One limitation of these past approaches is that these thermoplastic thrusters are designed for high impulse (e.g., thousands of seconds), but extremely low thrust, propulsion. Generally, such thrusters are not suited for high thrust aerospace and underwater propulsion, which require large flows of fuel to produce the thrust. Furthermore, combustion of fluoropolymers typically requires high pyrolysis temperatures (˜500° C.), and results in production of soot that is unacceptable on many missions, particularly space missions involving sensitive equipment. Combustion of polytetrafluoroethylene also tends to produce high molecular weight products that can limit propulsion performance (i.e., specific impulse).